Introduction
Chlorosulphonated polyethylene rubber (CSM) is a synthetic rubber, a product of chemical modification of polyethylene with chlorine and sulfur dioxide.
CSM is characterized by high heat resistance, wear resistance and flame retardancy. It is resistant to ozone, ultraviolet radiation, and weather factors. CSM with a high chlorine content (32–45%) is also fire-, oil- and petrol resistant. CSM based products have an especially high resistance to biocorrosion and high dielectric properties, and have good adhesion to various surfaces. In terms of resistance to aggressive mediums, CSM rubber surpasses polychloroprene, only falling behind in fire resistance, elasticity and frost resistance. In terms of gas permeability, CSM is superior to other rubbers except for butyl rubber [1].
CSM rubber based on high density polyethylene (Hypalon 40) is used for manufacturing a variety of technical rubber products: conveyor belt cover layer, wire and cable insulation, chemical resistant coating, liner of chemical equipment and shafts of papermaking machines, industrial hoses, belts, rubber compensators (vibration joints), heat-resistant seals, gaskets, sponge products, roofing and pond membranes, special types of rubberized fabrics.
Thanks to their insulating properties and low flammability, CSM based rubber is widely used as a material for cable insulation and sheathing [2].
The main function of magnesium oxide in chlorine and sulphonyl chloride containing CSM based rubbers is to remove acidic by-products (role of acid acceptor). Volatile acids are released in the processing, curing and aging of rubber products. Magnesium oxide neutralizes these acids and protects the rubber compound from degradation of rubber and scorching in the processing.
In addition to neutralizing acidic by-products, magnesium oxide can also be used in the production of CSM based rubbers as a curing agent. In a chemical reaction with moisture, MgO cross-links hydrated chlorine sulfonyl groups and forms ionic bonds. This makes it possible to achieve excellent physical and mechanical properties (except for compression set) [3].
The product under the trademark MagPro® is magnesium oxide with a high surface area obtained by indirect calcination of milled natural magnesium hydroxide (brucite mineral). The number in the MagPro® trademark name shows the typical particle surface area: 150 or 170 m2/g [4, 5].
The effect of various grades of magnesium oxide on the properties of CSM based cable sheathing compounds was studied. For the research, domestic brands of natural brucite-based magnesium oxide MagPro®150 and MagPro®170 were selected for comparison with Japanese synthetic magnesium oxide with a specific surface area of 150 m2/g.
Experimental part
| Parameter | MagPro®150 | MagPro®170 | Синт. MgO |
|---|---|---|---|
| MgO content, % (loss free basis) | 95.07 | 94.89 | 98.0 |
| CaO content, % | 2.55 | 2.57 | 0.78 |
| SiO2 content, % | 1.35 | 1.42 | 0.10 |
|
Fe2O3 content, % |
0.13 | 0.11 | 0.04 |
| Loss on ignition, % | 7.3 | 8.1 | 5.2 |
| Loose bulk weight, kg/m3 | 408 | 442 | 500 |
| Median particle size D50, µm | 8.6 | 8.6 | 8.2 |
|
Specific surface area, m2/g |
149.6 | 168 | 155 |
The rubber compounds were produced in a laboratory rubber mixer with the free chamber volume of 300 cm3, chamber temperature of 900°C, Banbury-type counter-rotating rotors, and rotation speed of the rotors of 30 rpm. The compounds produced in a rubber mixer were processed and formed into sheets on laboratory mills.
The industrial formulation of the CSM based cable sheathing presented in the table below was used for tests; the only changing was the grade of magnesium oxide.
|
|
Content, phr | ||
|---|---|---|---|
| Ingredient | MagPro®150 | MagPro®170 | Synthetic MgO |
| CSM rubber (chlorine content 35%, Mooney viscosity 56 MU) | 100.0 | 100.0 | 100.0 |
|
Magnesium oxide MagPro®150 |
5.0 | - | - |
|
Magnesium oxide MagPro®170 |
- | 5.0 | - |
| Synthetic magnesium oxide (Japan) | - | - | 5.0 |
| PE wax | 2.0 | 2.0 | 2.0 |
| HAF Carbon black N330 | 15.0 | 15.0 | 15.0 |
| Kaolin clay | 60.0 | 60.0 | 60.0 |
| Naphthenic process oil | 20.0 | 20.0 | 20.0 |
| Chlorinated paraffin (47% of Cl) | 15.0 | 15.0 | 15.0 |
| Antioxidant NBC | 1.0 | 1.0 | 1.0 |
| Pentaerythritol | 3.0 | 3.0 | 3.0 |
| Curing agent TMTD | 2.0 | 2.0 | 2.0 |
| Accelerator MBTS | 0.5 | 0.5 | 0.5 |
|
Total: |
223.5 | 223.5 | 223.5 |
The curing characteristics were determined using «MDR 3000 Professional» rheometer.
| Parameter | MagPro®150 | MagPro®170 | Синт. MgO |
|---|---|---|---|
|
Minimum torque МL, dN•m |
0.87 | 0.91 | 0.89 |
|
Maximum torque МH, dN•m |
5.03 | 5.43 | 4.79 |
| Min and Max torques Difference ΔМ, dN•m | 4.16 | 4.52 | 3.90 |
| Induction time Ts2, min | 2.99 | 2.69 | 2.79 |
| Optimum curing time, Tc90, min | 7.91 | 7.84 | 7.42 |
|
Curing rate index (CRI), min-1 |
20.33 | 19.42 | 21.60 |
The results show that curing induction time (Ts2) and the optimum curing time Tc90 practically do not depend on the grade of the studied magnesium oxide, as the difference does not exceed 3–7%.
Vulcanized specimens were produced by compression molding in hydraulic vulcanizing press. The pressure on the mold was at least 12 MPa.
Vulcanizates were tested a day after being produced for stress relaxation. Vulcanized specimens were also aged during 3 days in hot air or in mineral oil.
|
Properties |
Type and duration of exposure |
MagPro®150 |
MagPro®170 |
Synthetic MgO |
|
Tensile strength, MPa |
Original (before ageing) |
6,7 |
6,8 |
6,4 |
|
3 days, hot air at 150°С |
11,2 (+67%) |
9,1 (+34%) |
8,0 (+25%) |
|
|
3 days, mineral oil at 20°С |
8,0 (+19%) |
6,4 (-6%) |
6,4 (0%) |
|
|
Elongation at Break, % |
Original (before ageing) |
400 |
520 |
370 |
|
3 days, hot air at 150°С |
110 (-73%) |
65 (-88%) |
75 (-80%) |
|
|
3 дня, масло при 20°С |
380 (-5%) |
480 (-8%) |
320 (-14%) |
|
|
Tensile set, % |
Original (before ageing) |
70 |
52 |
58 |
|
3 days, hot air at 150°С |
10 (-86%) |
8 (-85%) |
8 (-86%) |
|
|
3 days, mineral oil at 20°С |
38 (-46%) |
30 (-42%) |
30 (-48%) |
|
|
Tear strength, kN/m |
Original (before ageing) |
20 |
28 |
27 |
|
3 days, hot air at 150°С |
14 (-30%) |
19 (-32%) |
18 (-33%) |
|
|
3 days, mineral oil at 20°С |
31 (+55%) |
31 (+15%) |
23 (-15%) |
|
|
Hardness, units Shore A |
Original (before ageing) |
64,5 |
64,9 |
65,2 |
|
3 days, hot air at 150°С |
73,5 (+14%) |
75,4 (+16%) |
70,0 (+7%) |
|
|
3 days, mineral oil at 20°С |
65,7 (+2%) |
66,6 (+3%) |
64,7 (-1%) |
|
|
Rebound elasticity, % |
Original (before ageing) |
16,6 |
15,7 |
15,7 |
|
3 days, hot air at 150°С |
16,6 (0%) |
15,5 (-1%) |
15,8 (+1%) |
|
|
3 days, mineral oil at 20°С |
16,6 (0%) |
15,7 (0%) |
15,7 (0%) |
| Characteristics | MagPro®150 | MagPro®170 | Синт. MgO |
|---|---|---|---|
| Change of mass, % | +0.7 | +0.7 | +0.65 |
| Change of thickness, % | +0.9 | +1.1 | +1.1 |
The swelling of vulcanizates in mineral oil is the same for all types of magnesium oxides studied: mass increase is about 0.7%, and the change of thickness of samples does not exceed 1.4%.
| Conditions | MagPro®150 | MagPro®170 | Синт. MgO |
|---|---|---|---|
| At 20°С | 1.6 | 1.7 | 1.7 |
| After 1 hour at 90°С | 1.8 (+12%) | 1.5 (-12%) | 1.9 (+12%) |
The results show that Volume resistivity of vulcanizates practically does not depend on the type of magnesium oxide used, and its change after exposure for 1 hour at 90°C remains within the same order of magnitude of measured value, i.e., 1010 Ohm·m.
Conclusion
1. Replacement of synthetic magnesium oxide with magnesium oxide (calcined brucite) MagPro®150 and MagPro®170 does not significantly affect the curing characteristics of rubber compounds and the mechanical properties of vulcanized CSM based cable sheathing rubber.
2. Ageing during 3 days in hot air at 150°C and in mineral oil at 20°C shows no significant difference between the oxides in terms of the changes in mechanical properties of all CSM-based cured stocks.
3. Mineral oil resistance at 20°C of vulcanizates is practically the same and does not depend on the type of magnesium oxide.
4. Volume resistivity of vulcanizates practically does not depend on the type of magnesium oxide used, and its change after exposure for 1 hour at 90°C remains within the same order of magnitude of measured value, i.e., 1010 Ohm·m.
References
1. Unabridged handbook of a rubber maker. In 2 parts / Edited by S.V. Reznichenko, Yu.L. Morozov. Volume 1. – M.: Techinform MAI Publishing Center LLC, 2012. – 744 p.
2. A.E. Kornev, A.M. Bukanov, O.N. Sheverdyaev “Technology of elastomeric materials”: Textbook for Universities – 3rd edition revised and expanded. – M.: NPPA Istek, Moscow, 2009. – 504 p.
3. Rubber technology: Compounding and Testing for Performance / Ed. by John S. Dick; Translated from English under the ed. of V.A. Shershneva – St. Petersburg.: Scientific foundations and technologies, 2010. – 620 p.
4. The official website of RMCC LLC. – URL: https://brucite.plus/upload/iblock/51b/magpro-150.pdf (accessed on 25.09.2024).
5. The official website of RMCC LLC. – URL: https://brucite.plus/upload/iblock/133/magpro-170.pdf
